1. Field of the Invention
The present invention relates to integrated circuits (IC), and more specifically to a method and apparatus for maintaining substantially constant trans-conductance value (for the contained transistors) without a substantial change in power consumption in the ICs.
2. Related Art
Integrated circuits are often used to implement components such as filters, amplifiers, etc. Typical integrated circuits are implemented using components such as trans-conductor circuits, which are characterized by trans-conductance. Trans-conductance generally is a measure of the responsiveness (degree of change) of current at an output to a change in the voltage at the input of a trans-conductor circuit as is well known in the relevant arts.
It is often desirable to maintain the trans-conductance of trans-conductor circuit s constant as is well known in the relevant arts. However, trans-conductance often changes during operation of integrated circuit due to reasons such as surrounding temperature and/or absence of manufacturing technology to attain a desired precision. Substantial changes in the trans-conductance value may be undesirable at least in some environments. Accordingly, it may be desirable to change the trans-conductance to revert back close to the original value.
One approach to changing the trans-conductance value of the MOS transistors based implementations is to change the voltage level Von (which equals (Vgsxe2x88x92Vt), wherein Vgs is the Gate To Source Voltage and Vt is the threshold voltage of the MOS) as is well known in the relevant arts. However, a problem with such an approach is that the electrical power consumed by the integrated circuit may increase substantially. Such increases in power consumption may be undesirable in many environments.
What is therefore required is, method and apparatus for controlling power in integrated circuits based on trans-conductor circuits.
The present invention allows a substantially constant trans-conductance value to be maintained associated with a trans-conductor circuit without a substantial increase in the electric power consumed by an integrated circuit containing the trans-conductor circuit. In an embodiment, the trans-conductor circuit is implemented using metal-oxide-semiconductor (MOS) transistors in which the trans-conductance value is given by the equation:
Gm=xcexc*COX*W/L*VONxe2x80x83xe2x80x83Equation (1)
wherein xe2x80x98Gmxe2x80x99 represents the trans-conductance value, xe2x80x98xcexcxe2x80x99 represents the mobility of holes/electrons in the transistor used to implement a trans-conductor circuit, xe2x80x98COXxe2x80x99 represents the channel capacitance per unit area of the transistor, xe2x80x98Wxe2x80x99 represents the width of the transistor, xe2x80x98Lxe2x80x99 represents the length of the transistor, and * represents a multiplication operation.
VON in turn may be represented by the following equation:
VON=V1xe2x88x92V3xe2x88x92VTxe2x80x83xe2x80x83Equation (2)
wherein xe2x80x98V1xe2x80x99 represents the voltage level at the gate terminal of the MOS transistor, xe2x80x98V3xe2x80x99 represents the voltage level at the source terminal of the MOS transistor, and VT is a threshold voltage of the MOS transistor.
The trans-conductance of a trans-conductor circuit (xe2x80x9cmain trans-conductor circuitxe2x80x9d) may decrease (change in general) when external factors such as temperature increases. The trans-conductance value may be increased to its original value by increasing xe2x80x98VONxe2x80x99. The electrical current flowing may also increase according to the following equation:
Electrical Current=K*W/L*Von2, wherein K=xcexc*COXxe2x80x83xe2x80x83Equation (3)
The increase in current leads to an increase in electrical power and may thus be undesirable. It may be noted that the power consumption increases proportionate to a square of Von.
According to an aspect of the present invention, an amount of current flowing in the circuit is compared with a reference current to determine whether the amount of current exceeds the reference current. The comparison is performed using an analog form of the reference current and the current in said integrated circuit.
Due to the comparison in analog form, an integrated circuit may be implemented using a fewer components. Usage of fewer components generally results in lower power consumption and lower noise.
If the current in the integrated circuit exceeds the reference current, an additional trans-conductor circuit is added which effectively increases the W/L of the MOS and hence the trans-conductance can be kept constant without changing Von. Von can then potentially be reduced (tuned) to attain a constant trans-conductance value.
Thus, in effect, a constant value of trans-conductance can be attained by increasing W/L instead of increasing Von. As the power consumption is proportionate to the square of Von, minimizing Von generally leads to substantial reduction in power consumption.
In an embodiment, the determination of whether the trans-conductance value has changed (warranting switching on of the additional trans-conductor circuit) is performed using one more trans-conductor circuit (xe2x80x9creplica trans-conductor circuitxe2x80x9d), which is implemented to have similar characteristics (xe2x80x9ctransfer functionxe2x80x9d in terms of converting voltage to current) as the operational trans-conductor circuit(s).
The replica trans-conductor may be operated using a D.C. voltage to determine whether the trans-conductance value has changed. Based on the determination in the replica trans-conductor circuit, the another trans-conductor circuit may be switched on/off.
Further features and advantages of the invention, as well as the structure and operation of various embodiments of the invention, are described in detail below with reference to the accompanying drawings. In the drawings, like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements. The drawing in which an element first appears is indicated by the leftmost digit(s) in the corresponding reference number.